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Edexcel Biology A Level > Chemistry for biologists > Flashcards

Chemistry for biologists Flashcards

1
Q

Why might a covalent molecule be slightly polarized

A

electrons are not evenly shared in the molecule. This separation of charge is known as a dipole and results in the molecule being slightly polarized.
these tiny charges are represented by S- and S+

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2
Q

What is dissociation

A

splitting of molecule into smaller atoms, molecules, or ions, especially by a reversible process.
example: dissolving an ionic substance in water

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3
Q

Is water a polar or non-polar molecule?

A

polar

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4
Q

Why is water a polar molecule

A

electrons are held closer to the oxygen atoms than the hydrogen atoms, resulting in a separation of charge

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5
Q

What is a hydrogen bond

A

weak electrostatic interMOLECULAR bonds formed between polar molecules containing at least 1 hydrogen atom

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6
Q

How does water form hydrogen bonds

A

slightly negative oxygen atom of one water molecule will attract the slightly positive hydrogen atoms of other water molecules in a weak electrostatic attraction

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7
Q

Why does water have a high melting and boiling point compared to other molecules of a similar size

A

it takes a lot of energy to break all of the hydrogen bonds that hold the molecules together

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8
Q

Why is water important

A

polar solvent

transport medium

Enables organisms to live in water, even in countries where it gets cold enough for the water to freeze in winter

Prevents the temperature of large bodies of water from changing drastically throughout the year, making it a good habitat

Important factor in hydraulic mechanisms in living organisms

Important in plant transport and in surface tension

Surface tension of water is important in plant transport systems and life on the surface of water masses

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9
Q

Why is water a polar solvent

A

Its covalent nature means water dissolves covalent compounds, its
polar nature means it dissolves ionic compounds

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10
Q

Why is water a good transport medium

A

dipole nature of water allows many substances to dissolve in it

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11
Q

How does water enable organisms to live in water, even in countries where it gets cold enough for the water to freeze in winter

A

At 4 degrees Celsius, water reaches its maximum density and as it cools further, molecules become more widely spaced and the water freezes into ice. Ice is less dense than water and floats above the water, forming an insulating layer helping to prevent the water beneath from freezing. Ice will also melt quickly as it is at the top and exposed to the sun

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12
Q

How does water prevent the temperature of large bodies of water from changing drastically throughout the year

A

water has a high specific heat capacity

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13
Q

Why is water an important factor in hydraulic mechanisms in living organisms

A

water cannot be compressed

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14
Q

What property of water is important in the movement of water from the roots to leaves of plants

A

water molecules are cohesive- the forces between the molecules mean they stick together

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15
Q

what property of water is important in plant transport systems and water tension

A

water molecules are adhesive- they are attracted to other different different molecules

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16
Q

Why does water have very high surface tension

A

attraction between water molecules, including hydrogen bonds, is greater than the attraction between water molecules and air. As a result, water molecules hold together forming a thin skin of surface tension

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17
Q

What is a dipole

A

The separation of charge in a molecule when the electrons in covalent bonds are not evenly shared

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18
Q

What is a macromolecule

A

a very large molecule formed by polymerization where monomers bond with many other similar units to make a very large molecule

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19
Q

What are carbohydrates made of

A

Carbon, Hydrogen and Oxygen

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20
Q

What are the three groups of carbohydrates

A

monosaccharides, disaccharides, and polysaccharides

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21
Q

General formula of monosaccharides

A

(CH2O)n

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22
Q

importance of triose sugars

A

important in mitochondria where the respiration process breaks down glucose into triose sugars

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23
Q

importance of pentose sugars

A

ribose and deoxyribose (which are pentose sugars) are important in the nucleic acids deoxyribonucleic acid and ribonucleic acid which make up the genetic material

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24
Q

what are the hexose sugars

A

best known monosaccharides, including glucose, fructose, and galactose. They have a ring structure

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25
Q

What are the isomers of glucose

A

a-glucose
B-glusose

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26
Q

What is the difference between the two isomers of glucose

A

have different arrangements of the atoms on the side chains of the molecule. The different isomers form different bonds between neighboring glucose molecules, and this affects the polymers that are made

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27
Q

What is a disaccharide

A

a sugar made up of two monosaccharide units joined by a glycosidic bond, formed by a condensation reaction

28
Q

What is a condensation reaction

A

a reaction in which a molecule of water is removed from the reacting molecules as a bond is formed between them

29
Q

what is a glycosidic bond

A

a covalent bond formed between two monosaccharides in a condensation reaction, which can be broken by a hydrolysis reaction to release the monosaccharide units

30
Q

What is sucrose’s source and its monosaccharide units

A

stored in plants such as sugar cane

glucose + fructose

31
Q

What is lactose’s source and its monosaccharide units

A

milk sugar- this is the main carbohydrate found in milk

glucose + galactose

32
Q

What is maltose’s source and its monosaccharide units

A

malt sugar- found in germinating seeds such as barley

glucose + glucose

33
Q

How are reducing sugars tested with benedicts reagent

A

Benedicts solution is a chemical reagent containing copper (ii) ions. Sugars such as glucose react when heated gently are reduce the copper (ii) ions into copper (i) ions forming a precipitate that changes colors from blue to orange and are hence called reducing sugars. All of the monosaccharides and disaccharides are reducing sugars except sucrose. it is known as a non-reducing sugar

34
Q

How are non-reducing sugars tested with benedicts reagent

A

The sucrose is heated with a few drops of HCl, cooled, and the solution is neutralized with sodium hydrogen carbonate to hydrolyze the glycosidic bonds. This produces monosaccharide units of the sugar, which give a positive benedicts test

35
Q

What are oligosaccharides

A

molecules with between 3-10 monosaccharide units (only molecules with 11 or more monosaccharides are known as true polysaccharides)

36
Q

What is hydrolysis

A

a reaction in which bonds are broken by the addition of a molecule of water

37
Q

What is ATP

A

adenosine triphosphate supplies energy and comes from the breakdown of the monosaccharide glucose, using oxygen, in the process of cellular respiration where chemical energy is TRANSFERRED from the glucose molecule to the ATP molecules

38
Q

which foods are good sources of relatively instant energy

A

foods containing monosaccharides and disaccharides

however, they cannot be stored as they are chemically active and are very soluble in water, so they will affect the water balance of cells

39
Q

why are polysaccharides ideal as energy storage molecules within a cell

A

1) very compact molecules which take up very little space
2) physically and chemically inactive, so they do not interfere with the other functions of the cell
3) not very soluble in water, so have almost no effect on water potential within a cell and cause no osmotic water movements

40
Q

What are the two compounds that starch is a mixture of

A

amylose
an unbranched polymer that spirals more as the chain lengthens which makes it more compact for storage. It has 1,4-glycosidic bonds
amylopectin
a branched polymer of glucose units with many terminal glucose units that can be broken off rapidly when energy is needed. Many glucose molecules are joined by 1,4-glycosidic bonds and also a few 1,6-glycosidic bonds, resulting in the branching chains

they are both long chains of a-glucose units

41
Q

Difference between amylopectin and glycogen

A

glycogen has many more 1,6-glycocidic bonds, giving it many more branches and allowing it to be broken down very rapidly

42
Q

What elements are lipids made of

A

hydrogen oxygen and carbon
(almost no oxygen)

43
Q

how does the amount of energy from lipids compare to that of carbohydrates

A

for the same amount of mass, lipids, especially triglycerides have almost 3 times as much energy

44
Q

List 2 differences between fats and oils

A

fats are solids at room temperatures and come mainly from animal sources
oils are liquids at room temperature and come mainly from plant sources

45
Q

What are lipids made up of

A

fatty acids and glycerol (propane-1,2,3-triol)

46
Q

How are lipids combined

A

using ester bonds

47
Q

what is glycerol’s formula

A

C3H8O3

48
Q

how are fatty acids structured

A

long hydrocarbon chain and a carboxyl group

49
Q

how can fatty acids vary

A

1) the length of the carbon chain can differ
2) the fatty acid may be saturated or unsaturated

50
Q

What is a saturated fatty acid

A

a fatty acid in which each carbon atom is joined to next one to it in the hydrocarbon chain by a single covalent bond

51
Q

What is an unsaturated fatty acid

A

a fatty acid in which the the carbon atoms in the hydrocarbon chain have one or more double covalent bonds in them

52
Q

What is a monosaturated fatty acid

A

a fatty acid with only one double bond in the hydrocarbon chain

53
Q

what is a polysaturated fatty acid

A

a fatty acid with two or more double covalent bonds between carbon atoms in the hydrocarbon chain

54
Q

How is triglyceride formed

A

when glycerol combines with 3 fatty acids in a condensation reaction between the carboxyl group of the fatty acid and the hydroxyl group of the glycerol. A molecule of water is removed and the bond formed is known as an ester bond. This type of condensation reaction is known as esterification

55
Q

Difference in the formation of solid and liquid lipids

A

lipids containing saturated fatty acids and have longer chain fatty acids are more likely to be solid at room temperature

56
Q

uses of proteins (7)

A

1) making hair, skin and nails
2) proteins make up the enzymes for metabolism and digestion
3) proteins make the hormones that control the different body systems
4) proteins enable the muscle fibers to contract
5) proteins make antibodies to protect you from disease
6) proteins helps blood to clot
7) protein, in the form of hemoglobin, transports oxygen

57
Q

Describe a single amino acids structure

A

A central carbon atom with a side group ( aka R group) (such as sulfur and selenium), an amine group (-NH2), a carboxyl group (-COOH), and hydrogen

58
Q

What is the role of the R group

A

it is not involved in the reactions which join the amino acids together, but the structure of the R group affects the way the amino acids interacts with others within the protein molecule. This mainly depends on whether the R group is polar or not

59
Q

What elements make up proteins

A

C, H, O, N and sometimes S

60
Q

How do amino acids join together

A

by a condensation reaction between the amino group one amino acid, and the carboxyl group of another, releasing a molecule of water. resulting in the formation of a dipeptide

61
Q

What is the name of the bond between 2 amino acids

A

a peptide bond

62
Q

What is a polypeptide

A

a long chain of amino acids joined by a peptide bond

63
Q

what is a dipeptide

A

two amino acids joined by a peptide bond

64
Q

when does a polypeptide form a protein

A

when the structure of the chain changes by folding or coiling or associates with other polypeptide chains

65
Q

how do hydrogen bonds form in amino acids

A

in amino acids,tiny negative charges are present on the oxygen of the carboxyl groups and tiny positive charges are present on the hydrogen atoms of amino groups. when these charged groups are s are close to each other, the opposite charges attract, forming a hydrogen bond.
Hydrogen bonds are weak but, potentially, they can be made between any two amino acids in the correct position, so there are many of them holding the protein together very firmly

66
Q

Why are hydrogen bonds important in proteins

A

important in the folding and coiling of polypeptide chains

67
Q

why are proteins affected by Ph and temperature

A

Hydrogen bonds break easily
and reform if pH or temperature conditions change.

Edexcel Biology A Level (3 decks)

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